Constant current open circuit protective system



y 1951 P. H. HOUSER ET AL 2,561,202

CONSTANT CURRENT OPEN CIRCUIT PROTECTIVE SYSTEM Filed Feb. 7, 1948Inventor: Philip H Mouser", Justin Peterson His Attorngy Patented ]uly17, 1951 CONSTANT CURRENT OPEN CIRCUIT PROTECTIVE SYSTEM Philip H.Houser and Justin Peterson, Swampscott, Mass., asslgnors to GeneralElectric Company, a corporation of New York Application February 7,1948, Serial No. 7,004

8 Claims. (Cl. 175-294) Our invention relates to electric protectivesystems, and more particularly to open circuit protective systems forconstant current circuits and the like.

In series circuits of the constant current type, such as are commonlyused for street and airport lighting and the like, electric translatingdevices of the resonant circuit type are often used to convert aconstant voltage input to a constant current output. It is acharacteristic of such constant current translating devices that if theoutput circuit is opened with the input circuit energized, there appearsat the output terminals a voltage considerably in excess of the normalfull load voltage. This high open circuit voltage is frequently of theorder of twice the full load voltage, and if the open circuit is due toa broken conductor, this full open circuit voltage appears across thebreak. Such a condition is highly undesirable in series circuits andaccordingly, it is advisable to provide some means for disconnecting theinput circuit of the translating device if the output circuit is brokenor opened for any reason.

Accordingly, it is a general object of our invention to provide a newand improved open circuit protective system for electric translatindevices.

It is anotherobject of our invention to provide a new and improved opencircuit protective system for series lighting circuits and the like.

It is a still further object of Our invention to provide a new andimproved open circuit protective system for constant current seriescircuits and the like.

It is a more specific object of our invention to provide, in a constantcurrent series lighting cir-' cuit or the like, means responsive to abreaking or other opening of the series output circuit for disconnectingthe constant current translating device from its supply'source.

Our invention will be more fully understood and its various objects andadvantages further appreciated by referring now to the followingdetailed specification, taken in conjunction with the accompanyingdrawing, the single figure of which is a schematic circuit diagram of aconstant current series lighting circuit including an open circuitprotective system embodying my invention.

Referring now to the drawing, we have shown by way of illustration ofone embodiment of our invention, a constant current series lightingsystem applicable to runway lighting for airports and the like. Thesystem illustrated comprises a plurality of series lighting loadcircuits l, 2 and}, arranged for selective connection through aplurality of manually operable switches 4, li, and 6 to a pair of outputterminals 1 and 8 of a constant current electric translating device 9.The translating device 9 is provided also with input terminals l0 and Hconnected through a circuit breaker l2 to a suitable source l3 ofsubstantially constant voltage single phase alternating current supplyof predetermined frequency.

The circuit breaker l2 connecting the input terminals of the translatingdevice 9 to the supply source I3 is of the manually operable, currentresponsively tripped type, and may suitably be a three-pole breakerhaving an operating handle in, contacts 14,15 and I6 and thermaltripping elements ll, l8 and I9, one associated with each pole of thebreaker, the thermal elements l1," l8 and I9 being connectedindependently to trip the breaker through a common tripping member. Asuitable breaker of this type is illustrated in Patent 2,047,816 issuedon July 14, 1936 to Atwood.

The supply source i3 is connected through two poles of the circuitbreaker l2 to a variable tap auto-transformer 20 provided with a tapselector switch 2i. The output terminals of the autotransformer 20 areconnected to the input terminals l0 and II of the translating device 9.

The constant current translating device 9 comprises a transformer 22having a variable tap primary winding 23 and a secondary winding 24. Theprimary winding is provided with a tap selector switch 23a. Thesecondary winding 24 is connected to an inductance 25 in series with 1av capacitor 26, and the output terminals 1 and 8 of the device are atopposite ends of the inductance 25. If desired, of course, only aportion of the inductance 25 need be included between the outputterminals 1 and 8. The transformer 22 and the inductance 25- are ironcore devices and may, if desired, be wound upon a unitary magneticstructure. Preferably, this magnetic structure is of the air gap type,such as illustrated in Patent 2,195,969, issued to Minor, on April 2,1.940.

When a translating device of the character described is so proportionedthat the reactances of the capacitor 26 and the inductance 25 aresubstantially equal and opposite at the supply source frequency, thedevice has the characteristic of translating a substantially constantvoltage alternating current input to a substantially constant currentalternating current output. It is a further characteristic of such adevice, however, that if the load circuit is opened. as by brokenconductor, or if the output terminals are otherwise open circuited whilethe input terminals are connected to the constant voltage supply source,the voltage appearing at the output terminals rises sharply to somethingof the order of twice the output terminal, voltage under full loadconditions. This open circuit output voltage is also distorted in shapeand contains prominent harmonics of the supply source frequency,principally the third harmonic.

The output terminals 1 and 8 of the translating device 8 are arranged tobe selectively connected to the series lighting load circuits i, I and 3through the manual selector switches l, I and 6. It will be observedthat if the switches I, I and I are all open, the load circuits I, 2 and3 are connected in series circuit relation across the load terminals 1and I. If however, any one or more of the selector switches I. 5 or 8 isclosed, the load circuit associated with each closed switch is shortcircuited.

Because of the open circuit output voltage characteristic of thetranslating device 8, it is desirable to provide means responsive to anopen load circuit condition for disconnecting the input terminals of thedevice 9 from the supply source 13. It will, of course, be appreciatedthat if the load circuit is broken for any reason and the outputterminals I and 8 thus left open circuited, the whole of the excessiveoutput terminal voltage appears across the break. This is a dangerousand undesirable condition in series circuits, and especially in seriesstreet or airport lighting circuits, where the high voltage across thebroken ends of the load circuit constitute a danger to service personnelor to passers-by, as well as a potential fire hazard.

In order to protect against such open circuit condition, we providemeans responsive to an open output circuit characteristic of thetranslating device 9 for disconnecting the device 8 from the supplysource. In the illustrated embodiment of our invention, we utilize thethird pole I6 and associate its thermal current responsive device I! ofthe circuit breaker l2. neither of which are connected in the singlephase supply circuit, for tripping the breaker in response to heatingcurrent supplied to the device l9 under open output circuit conditions.To provide such current, we connect the primary winding 21 of atransformer 2| across the input terminals Ill and II of the translatingdevice 9 in series with a normally open contact 29 of a control relay3!]. The secondary winding ll of the transformer 2| i connected to thethermal current responsive device I! in series circuit relation with thepole it of the circuit breaker l2. The actuating winding 32 of thecontrol relay 3|! is provided with a shunting capacitor 33a andconnected for energization to the output terminals 1 and l of the device9 through a tuning capacitor II. The inductance of the actuating winding32 and the capacitance of the capacitors 33 and Na are so proportionedthat the relay energizing circuit including these elements is resonantat the harmonic frequency prominent in the open circuit output voltageacross the terminals 1 and 0. whereby the relay 30 is significantlyresponsive only to this harmonic voltage. It will of course beappreciated by those skilled in the art that the resonant circuit32-43-3311 need not be connected directly across the terminals 1, I, butmay equally well be connected across any other portion of the loadcircuit or of the transformer secondary winding 24 or inductance 25, andwe intend in the appended claims to cover any such coupling to theoutput terminals 1, 8. I

In operation, when the translating device I i connected to its supplysource I I through the circuit breaker l2 and the output terminals I and8 are connected to a completed load circuit, the frequency of the outputvoltage is such that the tuned actuating circuit of the relay 3. isinsuiilciently energized to pick up the relay. If, however, the outputor load circuit is broken. the prominent harmonic frequency voltageappearing at the output terminals supplies sufllcient energizationthrough the tuned circuit 3243- 33a to pick up the relay ll, thereby toconnect the transformer primary winding 21 for energization across theinput terminals I! and H, and thus across the supply source B throughthe breaker i2. With the transformer 2| so connected, the transformersecondary winding 3| supplies an output current through the thermalcurrent responsive device I9 sufllcient to trip the circuit breaker I2,thereby to remove energizetion from the translating device 9 and thetransformer 28.

While we have described only a preferred embodiment of our invention byway of illustration. many modifications will occur to those skilled inthe art and we, therefore, wish to haveit understood that we intend inthe appended claims to cover all such modifications as fall within thetrue spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a constant current electric protective system, an electrictranslating device having input terminals for connection to a source ofalternating current supply of predetermined frequency and outputterminals for connection to a constant current load circuit, saidtranslating device having an electrical characteristic such that saidoutput terminals when open circuited supply a distorted voltagecontaining a prominent harmonic of said source frequency, switchingmeans for disconnecting said translating device from said supply source,and control means connected to actuate said switching means andincluding a circuit coupled to said output terminals and significantlyresponsive only to said harmonic frequency voltage.

2. In an electric protective system for a constant current load circuit,a constant current electric translating device having input terminalsfor connection to a source of alternating current supply ofsubstantially constant voltage and predetermined frequency and outputterminals for connection to a load circuit, said translating devicewhenso connected supplying a substantially constant current to said loadcircuit and having an electrical characteristic such that said outputterminals when open circuited supply a distorted voltage containing aprominent harmonic of said source frequency, switching means fordisconnecting said translating means from said supply source, andcontrol means connected to actuate said switching means and including acircuit coupled to said output terminals and significantly responsiveonly to said harmonic frequency voltage.

3. In a constant current electric protective system, an electrictranslating device having output terminals for connection to a constantcurrent load circuit and input terminals, switching means for connectingsaid input terminals to a source of alternating current supply ofpredetermined frequency, said translating device having an electricalcharacteristic such that when said input circuit is connected to saidsupply source and said load circuit open said output terminals supply adistorted voltage containin a prominent harmonic of said sourcefrequency, and means for disabling said switching means thereby todisconnect said translating device from said source comprising a controlcircuit coupled to said output terminals and resonont at said harmonicfrequency.

4. In a constant current electric protective system, an electrictranslating device having output terminals for connection to a constantcurrent load circuit and input terminals, switching means for connectingsaid input terminals to a source of alternating current supply ofpredetermined frequency, said translating device having an electricalcharacteristic such that said output terminals when open circuitedsupply a distorted voltage containing a prominent harmonic of saidsource frequency, thermal responsive means for disabling said switchingmeans thereby to disconnect said translating device from said supplysource, and means for energizing said thermal responsive meanscomprising a circuit resonant at said harmonic frequency and coupled forenergization to said output terminals.

5. In a constant current electric protective system, an electrictranslating device having output terminals for connection to a constantcurrent load circuit and input terminals, switching means for connectingsaid input terminals to a source of alternating current supply ofpredetermined frequency, said translating device having an electricalcharacteristic such that said output terminals when open circuitedsupply a distorted voltage containing a prominent harmonic of saidsource frequency, current responsive means for disablin said switchingmeans thereby to disconnect said translating device from said supplysource, and means for energizing said current responsive means includinga control circuit coupled for energization to said output terminals andsignificantly responsive only to said harmonic frequency voltage.

6. In a constant current electric protective system, an electrictranslating device having output terminals for connection to a constantcurrent load circuit and input terminals, a manually operable currentresponslvely tripped circuit breaker for connecting said input terminalsto a source of alternating current supply of predetermined frequency,said translating device having an electrical characteristic such thatsaid output terminals when open circuited supply a distorted voltagecontaining a prominent harmonic of said source frequency, and means foractuating the current responsive tripping means for said circuit breakerin response to opening of said load circuit comprising a source ofelectric current supply for said tripping means and means for renderingsaid last named current supply source effective in response to presenceof said harmonic frequency voltage at said output terminals.

7. In a constant current electric protective system, an electrictranslating device having output terminals for connection to a constantcurrent load circuit and input terminals, current responsively trippedswitching means for connectin said input terminals to a source ofalternating current supply of predetermined frequency, an electricalcharacteristic of said translating device being such that saidv outputterminals when open circuited supply a distorted voltage containing aprominent harmonic of said source frequency, a second source of electriccurrent supply for the current responsive tripping means of said circuitbreaker, and means coupled to said output terminals and significantlyresponsive to said harmonic frequency only for connecting said secondsupply source to said current responsive tripping means.

8. In an electric protective system for a constant current load circuit,a constant current electric translating device having output terminalsfor connection to said load circuit and input terminals, switching meansfor connecting said input terminals to a source of alternating currentsupply of substantially constant voltage and predetermined frequency,said translating device when so connected supplying a substantiallyconstant current to said load circuit and having an electricalcharacteristic such that when said load circuit is open a distortedvoltage containing a prominent harmonic of said source frequency issupply to said output terminals, current responsive tripping means forsaid switching means, and means for connecting said current responsivetripping means to a source of electric current supply including acontrol circuit resonant at said harmonic frequency and coupled to saidoutput terminals.

PHILIP H. HOUSER. JUSTIN PETERSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,298,665 Chubb Apr. 1, 19191,335,256 Peterson Mar. 30, 1920 1,821,342 Hellmund Sept. 1, 19312,177,900 Logan Oct. 31, 1939 2,226,041 Young Dec. 24, 1940 2,304,986Young Dec. 15, 1942 2,350,610 Haug June 6, 1944

